Toxic inorganic/organic substances in various water sources have to be reduced below regulated levels before the water goes into drinking water systems or is released into recipients.
Nitrate (NO3−) is the most common inorganic contaminant found in groundwater in the areas where agriculture activities occur heavily. Nitrates usually come from fertilizers, used in farming and gardening in order to provide the plants and shrubs with nutrients.
Other contaminants which may be generated from such activities are phosphates (PO43−) and traces of pesticides such as atrazine. Accumulation of fertilizers is a problem as they can go through the soil and contaminate ground water systems. Both shallow water wells and deep water wells can be affected.
Toxic metals such as arsenic (As), chromium (Cr), whereof its oxidation state +6 (CrVI) is regarded as most harmful, lead (Pb), mercury (Hg), cadmium (Cd), selenium (Se), etc., other substances as chlorinated hydrocarbons and other organic substances, sometimes measured as Total Organic Carbon (TOC) are generated either from natural origins or from industrial or farming activities.
In order to reach acceptable levels of contaminants in drinking water, several processes are currently used.
Reverse osmosis is based on the process of osmosis. This involves the selective movement of water from one side of a membrane to the other.
A major disadvantage of reverse osmosis is the large amount of contaminated wastewater generated, which can be as much as 50 to 90% of the incoming water. Over time, clogging of the membrane pores occurs as iron, salts and bacteria accumulate on the membrane surface. This not only affects the performance of the reverse osmosis system, but can also cause bacterial contamination of the water. This technique is also very energy consuming.
Distillation processes are also used. The nitrate and other minerals remain concentrated in the boiling tank. The disadvantages of this process include the amount of energy consumed (to boil the water), limited capacity and constant maintenance.
The ion exchange process percolates water through bead-like spherical resin materials (ion-exchange resins). Ions in the water are exchanged for other ions fixed to the beads. The two most common ion-exchange methods are softening and deionization. Ion exchange techniques also generate hazardous brine waste that needs to be deposited. Deionization (DI) systems effectively remove ions, but they do not effectively remove most organics or microorganisms. Microorganisms can attach to the resins, providing a culture media for rapid bacterial growth and subsequent pyrogen generation. This technique has a low initial capital investment but a high long-term operational cost.
US patent publication No. 2007/0241063A1 describes a process for treating water contaminated with a volatile organic compound with iron powder granules containing iron, carbon and oxygen. The carbon addition to the iron powder granules in US2007/0241063A1 is made during the atomization process and are not subjected to any mixing process. This is commonly known as a “pre-alloy” process in the field of powder metallurgy.
U.S. Pat. No. 5,534,154 describes a procedure for treating contaminated water by passing the water containing contaminant in solution through a permeable body of treatment material comprising particles of an adsorptive material physically mixed with particles of metal. The iron metal particles mentioned in the patent are iron fillings generally in solid granular form. The procedure requires a negative Eh voltage which in turn demands oxygen exclusion.
U.S. Pat. No. 6,827,757 describes a magnetite-iron based composite with very small average particle size of 0.05-10 μm.
EP 1273371A2 describes an iron powder adapted to remediate selected media by dehalogenating halogenated hydrocarbons in the media comprising iron powder particles and inorganic compounds. Said inorganic compounds should have a very low electric resistivity, preferably selected from the group consisting of Ca, Ti, V and Cr. Said inorganic compounds should be present on at least a portion of the surface of each particle.